The invention relates to a thin film transistor liquid crystal display (TFT LCD) device and in particular to a sealant region for encapsulating a liquid crystal display device.
A TFT LCD device is driven by voltage to emit light, and may be transmissive, reflective, or transflective.
A TFT LCD device suffers from degradation issues related to ambient environmental conditions such as moisture which may lead to performance loss, operational instability, poor color/emission accuracy, and shortened operational life. Specifically, water can cause crystallization and formation of organic solids, electrochemical reactions at the electrode-organic layer interface, corrosion of metals and migration of ionic species. To minimize such degradation, a TFT LCD device must be properly encapsulated to prevent moisture migration. Typical encapsulation methods utilize a color filter substrate covering the entire organic polymer areas with an adhesive sealant.
FIG. 1A is a top view of a sealant region of a conventional TFT LCD device.
As shown in FIG. 1A, a color filter substrate 10 is disposed over a TFT array substrate 2. Openings 4 are formed within a sealant region 6 distributed over the perimeter of the TFT array substrate 2. A sealant 14, as shown in FIG. 1C, encapsulates a TFT LCD device by contacting the color filter substrate 10 and TFT array substrate 2. Air is exhausted through trenches 12 when the sealant 14 is placed in the openings 4, preventing bubbles from forming in the sealant 14 or liquid crystal. In addition, openings 4 and trenches 12 are interconnected.
FIG. 1B is an enlarged view of the portion 8 of the sealant region shown in FIG. 1A. The sealant width is marked by distance g confined by the two vertical dotted lines.
FIG. 1C is a cross-section of the TFT LCD device shown in FIG. 1B along the plane defined by the horizontal dotted line AA′.
As shown in FIG. 1C, the openings 4 expose portions of the surface of the passivation layer 20, and the sealant 14 is placed in the openings 4. To place the sealant 14 between the TFT array substrate 2 and color filter substrate 10, the organic polymer layer 16 is selectively removed to form the openings 4. When the sealant 14 is placed in the openings 4, certain portions of the sealant 14 will rest on the neighboring and remaining organic polymer layer 16.
As shown in FIG. 1C, a TFT LCD device comprises the TFT array substrate 2, passivation layer 20, organic polymer layer 16, spacers 22 disposed over organic polymer layer 16, sealant 14, liquid crystal 18, and color filter substrate 10. Spacers 22 are disposed between the organic polymer layer 16 and color filter substrate 10 to maintain the cell gap.
The thickness of the sealant between the organic polymer layer 16 and color filter substrate 10 is difficult to apply in a precise manner. Moreover, as shown in FIG. 1C, the sealant must be evenly distributed on the organic polymer layer 16; otherwise defects such as mura will occur.
The large volume and thickness of the applied sealant may also lead to peeling of the sealant from the substrates. Such peeling will result in the loss of encapsulation integrity.
What is desirable is an improved method of encapsulating a TFT LCD device.